Digital Camera Help!?

I have a Canon Powershot SD750 Digital Camera, and I am attempting to connect an Audio Technica lavalier microphone to it. For some reason, even though the mic is switched on, the camera's microphone is used to record the audio instead of the mic I attached. How do I get this mic to work?? Thanks

try looking in the menu to see if you can switch them

Check for a download for an updated driver for the microphone or the camera.